Telephone system



Feb. 26,1924.

' 1,484,765 G. D. EDWARDS TELEPHONE SYSTEM Filed April 12, 1919 s Sheets-Sheet 1 -//4 van fan Gem 7e D. fdwm da Feb. 26,1924. mama;

G. D. EDWARDS TELEPHONE SYSTEM Filed April 12, 1919 3 Sheets-Sheet 2 A i y.

G. D. EDVJARDS TELEPHONE SYSTEM Febu 26', 1924.;

I 3 Sheets-Sheet 5 Filed April 12, 1919 v Patented Feb. 26, 1924.

UNETEE STATEd ldtdfitd FATEN'E QFFEEQ GEORGE D. EDWARDS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A. CORPORATION OF NEN' YORK.

TELEPHONE SYSTEM.

Application filed April 12, 1919.

To aZZ whom it may concern:

Be it known that I, GEORGE D. EDWARDS, a citizen of the United States, residing at East Orange, in the county of Essex, State of New Jersey, have invented certain new and useful Improvements in Telephone- Systems, of which the following is a full, clear, concise, and exact description.

The present invention relates to telephone systems and more particularly to train despatching and similar systems having a non-loaded copper metallic open wire circuit and in which a large number of stations are bridged across a common line of considerable length.

The principal object of the present in- .vention is to provide atelephone system of this type in which the transmission efficiency of all the stations of the system will be maintained sufficiently high for satisfactory operation and practically independent of the number of stations operatively connected with the common line at any one time. In accordance with this feature of the invention, the stations are each associated with the common line through respective bridge connections extendingbetween the line conductors; each bridge including receiving apparatus having impedance characteristics predetermined as conducive to maximum transmission efficiency under the conditions described. The absolute value of this impedance and the impedance angle are considerably higher than have been used here tofore in similar apparatus.

Another object of the present invention is to provide such a system in which the telephonic receiver and transmitter of the stations are inductively associated with the line through transformer coils and in which the transformer ratio of the coil can be varied from an efficient ratio from a receiv ing standpoint to another ratio more efficient from a transmitting standpoint. In accordance with this feature of the invention, the stations are inductively associated with the line through transformer coils having certain portions of their windings included in circuit normally during receiving, and means are provided to alter the circuits at each of the stations during transmitting to change the portions of the transformer windings in circuit at this time, in order to change the ratio of transf rmation Serial No. 289,867.

from one eflicient for receiving to one more efficient for transmitting.

Train despatching and similar telephone systems often include station selectors at the several stations which are connected to a bridge including impedance coils across the line at the respective stations, the point of connection being so chosen that the impedances between the selector and the respective sides of the line are substantially equal. It is advantageous that the same coils which are used to provide the impedance in the selector circuit should also serve as transformers for inductively associating the receiver and the transmitter of the station with the line and that the impedance of a station should be capable of variation de pending on whether such station is transmitting or receiving. It is highly desirable that the impedance balance between the selector at the station and the respective sides of the'line should be maintained independent of variation of the impedance of the station. A further object of the present invention accordingly is the provision of such a system in which the impedance balance between the selector of the station and the respective sides of the line thereat will be maintained independent of the variation of the impedance of the station and independent of whether such station is transmitting or receiving. In accordance with this feature of the invention, means are provided to vary the proportion of the transformer windings connected in the bridge of the line at a station to reduce or increase the impedance of the bridge thereat in such a way that the impedances between the selector and the respective sides of the line of said station are substantially equal independent of the variation of the transformer windings connected in bridge of the line at such station.

Referring to the drawings, Fig. 1 represents a telephone system embodying the present invention; Fig. 2 schematically illustrates a receiving circuit when receiving only; Fig. 3 a similar circuit when transmitting, and also shows the transmitting circuit at one of the stations in the system shown in Fig. 1; Fig. 4 illustrates a train despatching system equipped with selectors and embodying the present invention; Fig. 5 represents. a receiving circuit when receiv ing only; Fig. 6 illustrates a similar circuit when transmitting, this circuit also showing the transmitter circuit for the system shown in Fig. 4:; while Figs. 7 and 8, respectively, illustrate modifications of station circuits suitable for use in systems of the general type shown in Figs. 1 and 1.

Referring to Fig. 1, conductors 10 and 11 represent a pair of conductors providing a telephone line common to all the stations of the system, and the stations 13,13 and K indicate three of the stations thereof associated with the line at different points along its length. In train despatching systems, the length of the common line varies from about 25 miles in some installations to as high as 350 miles in others, while the number of stations associated with a system varies from as low as two or three in the shorter installations to as high as 50 or 60 stations on the longer lines. It is essential that satisfactory transmission be obtained at the most remote station of the line as well as at all intermediate stations under all conditions. Previous attempts have been made to attain this result by tapering the impedances of the several stations of the system so that each station would obtain sufficient energy for its operation without unduly diminishing the energy supplied to succeeding stations. This requires special design of each installation and the manufacture of special apparatus for use at the different stations, and in event of subsequent change in the number of stations or length of the line, entails re-design of the installation. and change in the apparatus of the different stations. This, obviously, is objectionable both from an operating and from a commercial standpoint. Commercial requirements make desirable a system in which standardized and identical apparatus can be employed which will be capable of satisfactory and efiicient application to the wide range of conditions met with in different installations, and in which the number of stations or length of line of any particular installation can be changed without re-design of the apparatus. With such a system standardized apparatus can be added to or re.- moved from the system, should the number of stations of the particular installation be increased or decreased.

The present system has been designed to efiiciently satisfy from a commercial standpoint the wide range of conditions encountered in practice and accomplishes the desired result through the proper selection of the impedances and the impedance angles of the receiving apparatus at the stations as hereinafter explained.

In the system shown in Fig. 1, the stations are associated with the line through transformers 12 bridged across the line at the respective stations. Each of the transformers 12 has four windings, two of the windings being serially connected in the bridge across the line, and the other two windings being serially connected in another circuit inductively associated with the bridge circuit. A conductor is secured to a point intermediate the two windings in the bridge circuit, and another conductor is connected between the two windings in the other circuit to enable the variation of the windings included in the respective circuits under varying conditions, as hereinafter explained. A condenser 1 is shown as provided in each bridge, and serves to prevent the passage of direct current across the bridge, this arrangement'being suitable if the line is also used for telegraphic transmission, or with selectors. The condenser can be omitted if the line is used only for telephonic transmission.

Each station is provided with a receiver 15, transmitter 16, key 17 battery 18, and a receiver switch 19 may also be employed to govern the association of the receiver 15 with the line. Assuming that the receiver switch 19 is closed, the receiver is normally included in a circuit such as shown in Fig. 2; extending through receiver 15, receiver switch 19,

both right-hand windings of its respective transformer 12, and the fourth and fifth'contacts of key 17; the bridge under these conditions including the condenser 1a in series with both left-handwindings or transformer 12 through the first and second contacts of the key 17. This represents the condition best adaptedto provide the maximum receiving efficiency, considering the system as a whole, and provides the correct predetermined impedance for the station.

For transmitting, the ratio of transformation of the coil 12 is changed from that used when receiving only, to a ratio more suitable for transmitting. In the system shown, to obtain the change in the ratio of transformation the normal impedance of the station is reduced and the transmitter 16 connected in circuit by depressing key 17 to talking position, thus removing the two upper windings of the transformer 12 from circuit and connecting the transmitter in series with the battery 18 and the lower right-hand winding of the transformer 12, and bridging the receiver 15 across the lower right-hand transformer winding. The station circuit under these conditions is schematically shown in Fig. 3. r

The transformers 12 are so designed that the effective impedance at telephonic frequencies of the station in the receiving condition shall have a correct and relatively high value, and so that theimpedance angle of the station shall have a proper high value which shall be conducive to the maximum transmission efficiency of the system. The capacitance of the condensers 14:, if used, is also chosen so that it will not unduly reduce the impedance nor the impedance angle of the station. Although the ideal impedance and impedance angle of the set in the receiving condition will vary in each particular case depending on the length of the line and number of stations, it has been found that a resultant station impedance of between five thousand and twenty thousand ohms at 800 cycles per second and having an impedance angle between and 88 degrees at the same frequency, is satisfactory, within the range of conditions likely to be met in practice. lVithin these ranges loss in transmission to the various stations of the system is not excessive, with due reference to the line and the number of stations employed. It was further found that to obtain maximum transmission efliciency for the system, the impedance within the limits given should vary approximately inversely as the variation of the impedance angles within the above limits. The station impedance best suited for general use appears to be between seven thousand and eight thousand five hundred ohms at 800 cycles with an impedance angle of between seventyfive and sixty-five degrees at the same frequency. These values are also particularly suitable from a commercial standpoint, as relatively inexpensive, and eificient apparatus can readily be designed to satisfy these re quirements.

The impedance of the two left-hand windings of the transformer may be of the same or difierent values, but the impedance of the upper windings would generally be much higher than that of the lower windings, so that upon .removal of the upper windings from circuit when transmitting in the system described, the impedance of the station is materially reduced, thus supplying increased energy to the line for transmission to other stations.

It will be noted that a high impedance bridge is normally present across the line at each station independent of whether or not the receiver 15 thereof is operatively associated with the line. Accordingly when voice currents are generated at any station they are impressed upon the line thereat and flow out over the line and divide through the high impedance bridges of the other stations; the high impedances of the stations preventing too great attentuation of the voice currents by the nearby stations and leaving ample energy for the .more remote stations.

The transmitting circuit at any station is designed to be closed only while the station is actually transmitting but the receiver thereat preferably remains connected in circuit during transmitting, so that another station is enabled to break in and to speak to the first station, while it is transmitting. Any suitable signaling arrangement can be used for intercalling between the stations of the system shown in Fig. 1 and one embodiment of a system providing for intercalling between stations through the use of selectors and selector keys at the different stations is illustrated in Figs. 4, 5 and 6 of the drawings.

In general, the system shown in Figs. 4, 5 and 6 is the same from a telephonic transmission standpoint as that shown in Fig. 1. The intercall system shown employs selectors 100, operated by impulses of alternate polarity developed as hereinafter described. The selector at each station controls a local circuit including a signal 101 at its station, but while the selectors of all the stations are operated when any station is called, the local circuit is closed and the signal 101 operated only at the, station whose code call corresponds to the particular set of calling impulses transmitted. The particular selector construction may be the same as that shown in United States patent to J. C. Field, No. 1,343,256, dated June 15, 1920, which however, forms no part of the present invention. With selectors of the above type, the two conductors 102 and 103 of the common line of the system serve in parallel for one side of the call circuit, while a third conductor, usually ground, provides the other side of the call circuit. A calling battery 104 is provided and the voltage thereof will be chosen to best suit the particular length of line used; in long lines the voltage being in the neighborhood of 300 volts. A relay 105 having a divided winding has the intermediate point thereof connected through one of its armatures to one side or the other of the battery 104, while its other armature connects an opposite side of the battery to the third conductor, depending on the position of the relay. One end of the winding is connected to the line conductor 102 through a retardation coil 106, while the other end of the winding is similarly connected to the other line conductor 103 through a battery 107 in series with another retardation coil 108. A condenser is bridged across the junction points of the retardation coils 106 and 108, and cooperates therewith to smooth out the impulses of current transmitted to the line conductors, thereby preventing interference with telephonic apparatus which may be connected therewith.

An inductance bridge is normally provided between the line conductors 102 and 103 at each station, including two condensers 109 and 110, and the four left-hand windings of a transformer 112; each bridge including the two upper left-hand windings of its transformer 112, in series relation with its two condensers 109 and 110, and the two lower left-hand windings of the transformer. One terminal of the main circuit of the selector 100 at each station is connected with the third conductor and the other terminal with the inductive bridge at a point between the condensers 109 and 110. A calling key 113 is employed at each station for calling any other station, and in practice may be a code calling key operable to send a variety of different sets of impulses, dependent on the code designation of the desired station. The closure of this key short-circuits the condensers 109 and 110, thereby establishing a direct current bridge across the line and operating the relay 105, as hereinafter explained.

To illustrate the calling operation of the system, assume that station C wishes to call station F. Sending key 113 is firstset to send aseries of impulses corresponding to the code designation of station F, and then operated to send out this series. Prior to the operation of the calling key at any station, the condensers 109 and 110 at all of the stations are charged positively from battery 104; the charging circuit extending from the positive side of battery 104 (the negative side of which is normally grounded through the lower normal contact of relay 105), thence in parallel through both portions of the winding of this relay, then through the retardation coils 106 and 108 and the line conductors 102 and 1031'sspectively in parallel, thence in parallel at the respective stations through theupper left-hand windings of the transformers 112 in series and through the lower left-hand windings of transformers 112 in series, rcspectively, to one side of the condensers 109 and 110; the other side of the respective condensers being connected in parallel to one terminal of the main circuit of the selectors 100, and through the selectors to ground.

Uponv the first closure of the key 113 at station C, a direct current circuit is completed to operate the relay 105; this circuit extending from one side of battery 107, both portions of the winding of relay 105 in series relation, retardation coil 106, conductor 102, thence through upper lefthand windings of transformer 112, contact of key 113 and lower left-hand winding of transformer 112 of station C, to conductor 103, and thence through the retardation coil 108 to the other side of battery. The operation of relay 105 reverses the connections of the calling battery 104 with respect to the line conductors 102 and 103 and with respect to ground; thereby simultaneously discharging the positive charge upon the condensers 109 and 110 at all the stations and charging them negatively. A current impulse isthus produced which passes through the selectors 100 and moves them all forward one step.

The operation of the key 113 at station 0 next opens the direct current circuit, whereupon the relay 105 is deenergized and returns to its normal position, again reversing the connections of the sending battery 104,

weaves thereby discharging the negative charge on the condensers 109 and 110 at the several stations and re-charging them positively. Another current impulse is thus produced which moves all the selectors forward another step. This operation is repeated upon each closure and interruption of the direct current circuit for the relay 105, by the operation of the key 113; the relay 105 thus serving as a pole-changer.

Upon completion of the selecting series of impulses the key 113 is ready to return to its original position, and the selector 100 of station F will have been stepped to the position in which it closes the local circuit of the call signal 101 thereat. In this position, the selector 100 at station F retains the local circuit closed to operate the signal 101 for a suitable length of time, after which the selector of station F is automatically restored to its initial position; while the selectors of the remaining stations are similarly restored to normal, although the local circuits thereat were not closed upon the calling of station F.

For satisfactory operation of the selectors, the impulses of the respective sides of the parallel branch circuit extending from the intermediate point of the winding of relay 105 to the intermediate point between the condensers 109 and 110 at station C should. be substantially equal at similar frequencies. The same is also true of the impedances of the respective sides of the parallel branch circuits of the other stations. The impedance of each side of the parallel circuit to one station may 'difier from the impedance of each side of the parallel circuit to another station, but the impedances of the two sides of the parallel circuit to any particular station should be substantially equal under any and all conditions. In the system shown, transformers 112 serve both as transformers for telephonic transmission and as impedances in the selector circuit; the two upper lefthand and the two lower left-hand windings respectively being normally included for this latter purpose in the upper and lower sides of the parallel circuit of the respective stations. The upper and lower left-hand windings of the transformers 112' at the sta tions are of substantially equal impedance under like conditions, and the two intermediate windings of the transformers 112 are also preferably of equal impedance relative to each other, while the retardation coils 106 and 108 are also preferably of equal impedance. The impedance balance between the respective sides of the parallel circuits is thus provided, and since the internal resistance of the battery 107, is extremely low this balance is not materially effected by the inclusion thereof in one side of the parallel circuit.

Each of the stations is provided with a receiver 115, a transmitter 116, talking key 117, battery 118, and a receiver switch 119 may also be provided to control the operative association of the receiver 115 with the line. With the receiver switch 119 closed, a normal receiving circuit, such as shown in Fig. 5, is provided; this circuit being practically the same from a telephonic standpoint as that shown in Fig. 2.

lVhen any station desires to talk, the key 117 thereat will be depressed, completing a transmitting circuit, removing the upper right-hand winding of the transformer 112 thereat from circuit, and bridging the receiver 115 across the lower right-hand winding of the transformer 112, in the same manner as described for the system shown in Fig. 1.' The upper and lower left-hand windings of transformer 112 are removed from the bridge across the line in this operation, thus changing the ratio of transformation of the transformer 112 to one bettersuited to the transmission of the outgoing energy developed by the transmitter 116, but without disturbing the impedance balance of the respective sides of the parallel branch circuits of the stations, inasmuch as the impedance of the windings removed from the bridge circuit are substantially equal and taken from different sides of the branch circuit at that station. Selector operation can accordingly take place at all the stations of the system independent of whether any particular station is in talking, normal receiving, or idle condition. The circuit condition of a station while talking is diagrannnatically illus trated in Fig. 6.

The systems shown in Figs. 1 and 4 are to be preferred as best meeting the operating requirements of systems of this kind, but other systems can also be provided in which through proper design of the receiver it can be bridged directly across the line without using a transformer inthe receiving circuit, although it is in general desirable to provide a transformer at each station to inductively associate the transmitter thereof with the line.

Examples of suitable station circuits are shown in Figs. 7 and 8; Fig. 7 showing one circuit in which no provision is shown by which intercalling between stations could be effected; and Fig. 8 showing a similar circuit in which a selector and calling key are provided at the station for intercalling between similar stations of such a system.

The receiver 150 and the condenser 151 bridged across the line conductors 152 and 153 as shown in Fig. 7 are designed to have a resultant impedance and impedance angle within the same limits as those found desirable for the resultant impedance and impedance angle of the two left-hand windings of thetransformer 12 in series with the condenser 14-, or independent thereof, depending on whether the condenser 14 is or is not used in the system shown in Fig. 1. Should the condenser 151 be omitted the impedance and the impedance angle of the receiver itself are designed to fall within the above limits; namely, between five thousand and twenty thousand ohms impedance at 800 cycles and between an im pedance angle of fifty-five and eighty-eight degrees at the same frequency. This impedance of the receiving circuit is, at any frequency, maintained substantially constant at any station independent of talking at that station inasmuch as a separate circuit for transmitting is provided. On closure of the key 15 1, a local circuit is completed from local battery 155, through the primary winding of transformer 156, lower contacts of key 15%, and transmitter 157, to battery. The closure of the upper contacts of key 154: bridges a secondary. winding of the transformer 156 across the conductors 1.52 and 153 at the transmitting station; whereby current variations corres aonding to those developed by the transmitter 157, are impressed upon the line. Since the transformer 156 has a proper transformation ratio, suiiicientenergy will be supplied to the line to etliciently operate the receivers of all the stations of the system.

In the station circuit shown in Fig. 8 the windings of the receiver 160 and the condensers 161 and 162 are serially bridged across the line conductors 163 and 16 1; the bridge extending from conductor 163, through upper winding of receiver 160, condensers 161 and 162, and lower winding of receiver 160 in series aiding relation to the upper winding, to conductor 16 1-. The selector 165 has one terminal connected to the bridge intermediate the condensers .161 and 1.62, and has the other terminal connected to ground or to a third conductor, as outlined in the description of the system shown in Fig. 1. The selector 165 controls the local signal 166 and a selector key 167 serves, on closure, to short-circuit the condensers 161 and 162 from the bridge circuit, thus completing a direct current circuit to operate a relay (not shown), corresponding to the relay 105 of Fig. 4, which selectively operates the selectors of the different stations, as previously described. The necessary impedance balance is obtained by making the impedance of the upper winding of the receiver 116 and the capacitance of the condenser 161, substantially equal, respectively, to the impedance of the lower winding of the receiver and the capacitance of the condenser 162. While the windings of the receiver rein series aiding relation, as regards telephonic currents, they are in parallel opposing relation as pan regards calling current for the selectors, and the consequent neutralization of the magnetic flux, developed by the passage of calling current through the two windings, prevents objectionable noises in the receiver, in dependent of the operation of the selectors. The transmitting circuit of the station of the system shown in Fig. 8 is identical with that shown in Fig. 7 and accordingly no separate explanation thereof is considered necessary.

What is claimed is:

1. A telephone system comprising a plurality of stations, a pair of conductors common to the stations, a bridge circuit at each of the stations individualthereto and extending between the conductors, and receiving apparatus individual to each of the stations and included in the bridge circuit thereof; the resultant impedance of each of the bridge circuits lying between five thousand and twenty thousand ohms at 800 cycles per second, and the resultant impedance angle thereof lying between fiftyfive and eighty-eight degrees at the same frequency.

2. A telephone system comprising a plurality of stations, a pair of conductors common to the stations, a bridge circuit at each of the stations individual thereto and extending between the conductors, and receiving apparatus individual to each of the stations and included in the bridge circuit thereof; the resultant impedance of each of the bridge circuits lying between seven thousand and eightthousand five hundred ohms at 800 cycles per second, and the resultant impedance angle thereof lying between sixty-five and seventy-five degrees at the same frequency.

'3. A telephone system comprising a plurality of stations, a pair of conductors com.- mon to the stations, receiving apparatus in dividual to each of the stations, a condenser individual to each of the stations, and a bridge circuit at each of the stations individual thereto extending between the conductors and including the receiving apparatus and the condenser in series therein; the receiving apparatus and the condenser being so proportioned that the resultant impedance of each of the bridge circuits lies between five thousand and twenty taousand ohms at 800 cycles per second, and so that the resultant impedance angle of each of the bridge circuits lies between fifty-five and eighty-eight degrees at the same frequency.

4. A telephone system comprising a plurality of stations, a pair of conductors com mon to the stations, receiving apparatus individual to each of the stations, a condenser individual to each of the stations, and a bridge circuit at each of the stations individual thereto extending between the con ductors and including the receiving apparm tus and the condenser in series thein; the

Laser/es receiving apparatus and the condenser being so proportioned that the resultantimpedance of each of the bridge circuits lies between seven thousand and eight thousand five hundred ohms at 800 cycles per second, and so that the resultant impedance angle of each of the bridge circuits lies between sixty-five and seventy-five degrees at the same frequency.

5. A telephone system comprising a plurality of stations, a pair of conductors connecting the stations, transformers indi vidual to each of the stations and each having a plurality of windings inductively associated, a bridge circuit individual to the stations extending between the conductors and including therein a portion of the windings of the transformer individual thereto, telephone receivers individual to each of the stations, and circuits individual to each of the stations including therein the telephone receiver and another portion of the wind ings of the transformer individual thereto to inductively associate the receiver with the conductors; the resultant impedance of each of the bridge circuits lying between five thousand and twenty thousand ohms and the resultant impedance angle of the bridge circuits lying from fiftydive and eighty-eight degrees at the same frequency.

6. A telephone system comprising a plurality of stations, a pair of conductors connecting the stations, transformersindividual to each of the stations and each having a plurality of windings inductively associated, bridge circuits individual to the stations extending between the conductors and includ ing therein a portion of the windings of the transformer individual thereto, telephone receivers individual to each of the stations, and circuits individual to each of the stae tions including therein the telephone receiver and another portion of the windings of. the transformer individual thereto to inductively associate the receiver with the conductors; the resultant impedance of each of the bridge circuits lying between seven thousand and eight thousand five hundred ohms at 800 cycles per second, and the resultant impedance angle of each of the bridge circuits lyingcbetween sixty-live and seventy-five degrees at the same frequency.

7. A telephone system con'iprising a plurality of stations, a pair of conductors common to the stations, transformers individual to each of the'stations and each having a plurality of windings inductively associated, a condenser individual to each of the stations, bridge circuits individual to the stations extending between the conductors and including serially therein a portion of the windings of the transformer and the condenser individual thereto, telephone receivers indi *idual to each of the stations, and circuits individual to each of the stations in eluding therein the receiver and another portion of the windings of the transformer individual thereto to inductively associate the receiver with the conductors; the portion of the respective transformer windings included in the bridge circuits and the respective condenser being so proportioned that the resultant impedance of each of the bridge circuits lies between five thousand and twenty thousand ohms at 800 cycles per second, and so that the resultant impedance angle thereof lies between fifty-five and eight-eight degrees at the same frequency.

8. A telephone system comprising a plurality of stations, a pair of conductors common to the stations, transformers individual to each of the stations and each having a plurality of windings inductively associated, a condenser individual to each of the stations, bridge circuits individual to the stations extending between the conductors and including serially therein a portion of the windings or the transformer and the condenser individual thereto, telephone receivers individual to each of the stations, and circuits individual to each of the stations including therein the receiver and another portion of the windings of the transformer individual thereto to inductively associate the receiver with the conductors; the portion of the respective transformer windings included in the bridge circuits and the respective condenser being so proportioned that the resultant impedance of each of the bridge circuits lies between seven thousand and eight thousand five hundred'ohms at 800 cycles per second, and so that the resultant impedance angle thereof lies between sixty-five and seventy degrees at the same frequency.

9. A telephone station circuit comprising a pair of conductors, a transformer individual to the station, and having a plurality-of windings inductively associated, a' bridge circuit extending between the conductors and including a portion of the transformer windings therein, areceiver, a transmitter, a source of current, a second circuit including the receiver, the transmitter, the source of current, and another portion of the transformer windings therein to inductively associate the receiver and transmitter with the conductors, and means to change the portion of the windings included in both of the circuits to change the transformer ratio for transmitting.

10. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, .a source of current, a second circuit including the receiver and another portion of the transformer windings, means to include the transmitter and source of current in the second circuit, and means to remove a portion of the transformer windings from the bridge circuit.

11. A telephone station circuit comprising a pair ofconductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and another portion of the transformer windings, and means to simultaneously include the transmitter and source of "current in the second circuit and to remove a portion of the transformer windings from the bridge circuit.

12. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and another portion of the transformer windings; and means to simultaneously remove a portion of the transformer windings from the second circuit and from the bridge circuit.

13. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and another portion of the transformer windings, and means to simultaneously include the transmitter and source of current in the second circuit and to remove a portion of the transformer windings from both the second circuit and from the bridge circuit during the inclusion of the transmitter in the second circuit.

1 1. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and another portion of the transformer windings, means to include the transmitter and source of current in the second circuit, and means to remove aportion of the transformer windings from the bridge circuit upon the inclusion of the transmitter and source of current in the second circuit during the inclusion of the transmitter in the second circuit.

15. A telephone station circuit comprising 7 the receiver across said last mentioned transa pair of conductors, atransformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit includ ing the receiver and another portion of the transformer windings, means to include the transmitter and source of current in the sec-- ond circuit, and means to remove a portion of the transformer windings from the bridge circuit upon such inclusion;

16. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and having a plurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and anotherportion of the transformer windings, means to simultaneously include the transmitter and source of current in the second circuit, to remove a portion of the transformer windings from the second circuit and to remove a portion of the transformerwindings from the bridge circuit. p

17. A telephone station circuit comprising a pair of conductors, a transformer indi vidual to the station and having aplurality of windings inductively associated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter,

a source of current, a second circuit includng portion-of the transformer windings in the second circuit, means to include the source of current and transmitter in the second circuit in serial relation with a portion of the transformer windings in said second circuit and to bridge in the receiver and another former windings, and means to remove a portion of the transformer windings from the/ bridge circuit upon the inclusion ofthe transmitter in the second circuit.

18. A telephone station circuit comprising a pair of conductors, a transformer individual to the station and'having a plurality of windings inductivelyassociated, a bridge circuit extending between the conductors and including a portion of the transformer windings therein, a receiver, a transmitter, a source of current, a second circuit including the receiver and anotherportion of the transformer windings, and means to simultaneously remove a portion of the transformer windings from the second circuit, to include the source ofcurrent and transmitter in the second circuit in serial relation with the portion of the transformer windings remaining therein, to bridge the receiver across the portion of the transformer windings remaincuit intermediate difierent impedance wind mgs therein and the third conductor, and means to alter the portion of the impedancewindings included in the bridge" circuit between the point of connection of the signal apparatus therewith and each of the conductors of the pair to alter the impedance without changing the impedance ratio of the respective portions of the bridge circuit be-' tween the point of connection and the respective conductors of the pair.

20. A station circuit comprising a pairof' conductors, a bridge circuit extending be-- tween the palr of conductors, a plurality of" impedance windings included in the bridge c1rcu1t,-a th rd conductor, signal apparatus connected between a point of the bridge circuit intermediate difierent impedance windings therein and the third conductor, and means to alter the'portion of the impedance windings. included in the bridge circuit between the point of connectionof the signal apparatus therewith and each of the conductors of the pair to alter the impedance of the respective portions of the bridge circuit between the point of connection and the respective conductors of. the pair-by substantially equal decrements.

21. A station circuit comprising a pair of conductors, a bridge circuit extending between the pair of conductors, a plurality of impedance windings in the bridge'circuit, a third conductor, signal apparatus connected between a point of the bridge circuit intermediate different impedance windingstherein and the third conductor, means to remove a portion of the impedance windings included in the bridge circuit between the point of connection of the signal apparatus therewith and each of the conductors of the pair to correspondingly reduce the impedance of the respective portions of the bridge circuit between the point of connection and,

the respective conductors of the pair.

22. AStSi/IOH circuit comprising a pair of conductors, a bridge circuit extending be the point of connection of the signal apparatus therewith and each of the conductors of the pair to reduce the impedance of the respective portions of the bridge circuit between the point of connection and the respective conductors of the pair by substantially equal amounts.

23. A station circuit comprising a pair-of conductors, a bridge circuit extending between the pair of conductors, a plurality of impedance windings included in the bridge circuit, a third conductor, signal apparatus connected between a point of the bridge circuit intermediate different impedance windings therein and the third conductor, the portion of the impedance windings included in the respective portions of the bridge circuit between the point of connection and the respective conductors of the pair being of substantially equal impedance, and'means to alter the portion of the impedance windings included in each ofrthe respective portions of the bridge circuit to alter the impedance of the respective portions thereof by substantially equal amounts to maintain a substantial impedance balance between the respective portions of the bridge circuit.-

Q. A station circuit comprising apair of conductors, a bridge circuit extending between the pair of conductors, a plurality of impedance windings included in the bridge circuit, a pair of condensers oi substantially equal capacitance, a bridge circuit including a portion of the impedance windings in serial relation withthe pair of condensers and another portion of the impedance windings, a third conductor, signal apparatus connected between apoint of the bridge cir cuit intermediate the pair of condensers and the third conductor, the portion of the impedance windings included in the respective portions of the bridge circuit betweenthe point of connection and the respective conductors of the pair being of substantially equal impedance, and means to alter the portion of the impedance windings included in each of the respective portions of the bridge circuit to alter the impedance of the respective portions thereof by substantially equal amounts to maintain a substantial balance between the respective portions of the bridge circuit.

25. A telephone system comprising a pair ofconductors providing a telephonic circuit between a plurality of stations, a bridge circuit extending across the pair of conductors and individual to one of the stations, telephonic receiving apparatus individual to said station and having a plurality of impedance windings included in the bridge circuit, a third conductor, signal apparatus connected between a point of the bridge circuit intermediate different impedance windings therein and the third conductor, a second bridge circuit between the pair of conductors, a source of signaling current positioned between a point of the second bridge circuit and the third conductor, the impedance between the points of connection of'the bridge circuits over one of the pair of conductors being substantially equal to the. impedance between the'points of connection of the bridge circuits over the other conductor of the pair during signaling, a signaling circuit including in parallel respective portions of the bridge circuits and the respective conductors of the pair forv one side thereof and the third conductor for the other side thereof, means to control the application of the source of signaling current to the signaling circuit to operate the signaling apparatus at said station, and means to alter the portion of the impedance windings included in the bridge circuit of such station between the point of connection with the signal apparatus therewith and each of the conductors to the pair. to change the impedance of the respective portions of such bridge circuit by substantially equal amounts; whereby the impedance of the receiving apparatus can be materially altered without substantially afiecting the impedance balance of the parallel portion of the signaling circuit.

26. A telephone system comprising a pair of conductors providing a telephonic circuit between a plurality of stations, abridge circuit extending across the pair of conductors and individual to one of the stations, telephonic receiving apparatus individual to said station and having aplurality ofimpedance windings included in the bridge circuit, a third conductor, signal apparatus at said station connected between a point of the bridge circuit intermediate different impedance windings therein and the third conductor, a second bridge circuit between the pair of conductors, a source of signaling current positioned between a point of the second bridge circuit and the third conductor, the impedance between the points of connection of the bridge circuits over one of the pair of conductors being substantiallyequal to the impedance between the points of connection of the bridge circuits over the other conductor of'the pair during signal ing, a signaling circuit including in parallel respective portions of the bridge circuits and the respective conductors of the pair for one side thereof and the third conductor for the other side thereof, means to control the application of the source of signaling current to the signaling circuit, and means to reducethe portion of the impedance windings included in the respective portions of the bridge circuit of such station to reduce the impedance of such respective portions by substantially equal amounts; whereby the impedance of the bridge circuit can be ma- ZEL ' terially reduced without substantially affecting the impedance balance of the parallel portion of the signaling circuit.

- 27. A telephone station circuit comprising a'pair of conductors extending to another station, a bridge circuit extending be- .tweenthe pair of conductors, telephonic receiving apparatus having a plurality. of impedance windings included in the bridge circuit, a third conductor, signal apparatus connected between a point of thebridge circuit intermediate different impedance windings therein and the third conductor, the portion of the impedance windings included in the respective portions of the bridge circuit between the point of connection and the respective conductors of the pair being of substantially equal impedance, and means to alter the portion of impedance windings in each of the respective portions of the bridge circuit to alter the impedance of such respective portions by substantially equal amounts to vary the impedance of the bridge circuit without substantially affecting the impedance balance of the respective portions of the bridge circuit for the operation of the signal apparatus. V.

28. A telephone system comprising a pair of conductors providing a telephonic circuit between a plurality of stations, a bridge circuit extending across a pair of conductors and individual to one of the stations, a transformer having a plurality of windings inductively associated and having a portion of the windings included in the bridge circuit, a telephone receiver, another circuit including the receiver and another portion of the transformer windings therein, a third conductor, signal apparatus at such station con nected between a point of the bridge circuit intermediate the transformer windings included therein and the third conductor, a second bridge circuit between the pair of conductors, a source of signaling current between a point of the second bridge circuit and the third conductor, the impedance between the points of connection of the bridge circuits over one of the pair of conductors being substantially equal to the impedance between the points of connection of the bridge circuits over the other conductor of the pair, a signaling circuit including in parallel the respective portion of the bridge circuits and the respective conductors of the pair for one side thereof and the third conductor for the other side thereof, means to control the application of the source of signaling current to the signaling circuit, and means to reduce the portion of the transformer windings included in the respective portions of the bridge circuit of such station to reduce the impedance of the respective portions of such bridge circuit by substantially equal amounts; whereby the impedance balance of assa/c5 the parallel portion of the signal circuitis not substantially affected. t

29. A telephone system comprising a pair of conductors providing a telephonic circuit between a plurality of stations, abridge circuit extending between the pair of conductors and individual to one of the stations, a transformer having a plurality of windings inductively associated and having a portion of the windings included in the bridge cirv cuit, a telephone receiver, a transmitter, a source of current, anothercircuit including the receiver, the transmitter, the source of current and another portion of the transbeing substantially equal to the impedance between the points of connection of the bridge circuitsover the other conductorof the pair during signaling, a signaling circuit including in parallel the respective portions of the bridge circuits and the respective conductors of the pair for one side thereof and the third conductor for the other side thereof, means to control the application of the source of signaling current to the signaling circuit, and means to remove a portion of the transformer windings included in the respective portions of the bridge circuit of such station to reduce the impedance of the respective portions of such bridge circuit by substantially equal amounts; whereby the resultant impedance of such bridge circuitis materially reduced for telephonic transmission without substantially affecting the impedance balance of the parallel portion of the signaling circuit.

30. A telephone system comprising, a pair of conductors providing a telephonic circuit between a plurality of stations, a bridge circuit extending between the pair of conductors at one of the stations, a transformer having a plurality of windings and having a portion of the windings included in the bridge circuit, a receiver, a transmitter, a source of current, another circuit including the receiver and another portion of the trans former windings, a third conductor, signal apparatus connected between a point of the bridge circuit intermediate the transformer windings therein and the third conductor, a second bridge circuit between the pair of conductors, a source of signaling current positioned between a point of the second bridge circuit and the third conductor, the impedance between the point of connection of the bridge circuits over one of the pair of conductors being substantially equal to the impedance between the points of connection of the bridge circuits over the other conductor of the pair during signaling, a signal circuit including in parallel the respective portions of the bridge circuits and the respective conductors of the pair for one side thereof and the third conductor for the other side thereof, means to control the application of the source of signaling current to the signal ing circuit, means to include the transmitter and source of current in such other circuit, means to remove a portion of the transformer winding from such other circuit upon such inclusion, and means to remove a portion of the transformer windings included in the first bridge circuit between the point of connection of the signal apparatus therewith and each of the conductors of the pair upon the inclusion of the transmitter in such other circuit to reduce the impedance of the respective portions of such bridge circuit by substantially equal amounts; whereby the impedance balance of the parallel portion of the signal circuit is not substantially afiected on the inclusion of the transmitter in such other circuit.

In witness whereof, I hereunto subscribe my name this tenth day of April, A. D. 1919.

GEORGE D. EDWARDS. 

